During a cold startup of a fuel cell stack at a temperature below freezing, it is not possible to extract a desired power generation amount from the fuel cell stack because moisture which was previously produced in the fuel cell during power generation freezes. Even if fuel gas is supplied to the fuel stack, since the reaction face (or membrane electrode assembly) is covered with ice, it is impossible to supply the reaction face with a sufficient amount of fuel gas. U.S. Pat. No. 6,358,638B1 and 6,103,410 disclose a technique for improving startup of a cell fuel stack at a temperature below freezing. The technique disclosed in U.S. Pat. No. 6,358,638B1 melts ice using combustion heat produced in a fuel cell by allowing a small amount of hydrogen or air to flow into the anode or the cathode. The technique disclosed in U.S. Pat. No. 6,103,410 promotes melting of ice in the fuel cell stack by introducing a gaseous mixture of hydrogen gas and air into the cathode and thus performing catalytic combustion of the gaseous mixture in the cathode.